1. Field of the Invention
This invention relates to a micro-mirror applied to a MEMS (Micro Electro Mechanical Systems) and a method for fabricating such micro-mirror, and particularly this invention relates to a micro-mirror suitable for document scanning application and a method for fabricating the same.
2. Description of the Related Art
A micro-mirror (namely, a scanning mirror) is fabricated by a micro machining using a silicon substrate as a part applied to a laser scanner, for example. In a conventional micro-mirror such as described in an article [Technical Digest of the 16th Sensor Symposium, 1998 pp. 167–170], for example, a flat surface section of a silicon substrate is made to be a mirror surface in almost of all the micro-mirrors. In this case, on an upper substrate made of silicon, a micro-mirror and a hinge section for supporting the micro-mirror on the upper the substrate are fabricated by an-isotropic etching process, and the micro-mirror vibrates by an electro-static power acting between an electrode formed on a lower substrate and an electrode provided on the upper substrate in a direction perpendicular to the upper substrate with the hinge section as a center.
Incidentally, the conventional micro-mirror as described above has advantages such that a fabricating process is simple because of its simple construction. On the contrary, as the flat surface of the substrate is directly utilized, its deflection angle is limited to a certain limited extent, so that a scanning area or extent is restricted when used as a scanner. Conventionally, it is proposed to provide a slant surface on a substrate and a scanning mirror is set on the slant surface as a scanner (U.S. Pat. No. 5,966,230 or Japanese Laid-open Publication H7-199,103). In this article, the scanner is used as a bar-code reader, and in this case, the slant surface having an angle of 45 degrees relative to the flat section is at first formed on the substrate, and then the scanning mirror supported by an intolerance hinge section is provided at the slant surface, thereby the scanning mirror is made rotatable by an electro-static power with the intolerance hinge section as a center.
But in a particular application such as the bar-code reader, it is requested to be able to scan a target moving to all directions, to accept any shape of the target, to perform a high speed scanning of the target moving in a short time, etc. so that it is desired to enlarge the deflection angle of the micro-mirror. In the above-mentioned scanner, a deflecting direction of the scanning mirror is also substantially perpendicular to the top surface of the slant surface, and the rotation angle thereof is limited thereby.
Further in the conventional micro-mirror, the hinge section is fabricated by forming an aperture by etching, but generally, defects are frequently generated at corners of the aperture, so that if the aperture is formed only within a single surface (crystalline plane) as conventional, it causes a problem where the hinge section is tend to be destroyed by the concentration of the stress at the defect section upon driving. Further, there exists another problem where a dimensional accuracy of the hinge section is largely degraded by over-etching upon forming the aperture.